PROJECT SUMMARY The objective of this proposal is to develop potent and selective inhibitors of the kinase, DYRK1A, to treat mild to moderate Alzheimer's disease (AD). A compelling body of data points to hyperphosphorylated tau species as mediators of toxicity in AD. p-Tau species may significantly impact a number of cellular events. Prominently, they participate in the formation of neurofibrillary tangles (NFTs), whose presence is closely linked with disease progression. An important question that remains is how tau is hyperphosphorylated. DYRK1A is a dual specificity kinase for which tau serves as a substrate. DYRK1A activity may be involved in AD pathogenesis because: (1) DYRK1A is a kinase for which tau serves as substrate; (2) it is robustly expressed in CNS neurons; (3) increased DYRK1A immunoreactivity is found in AD in the cytoplasm and nucleus of neurons of the entorhinal cortex, hippocampus and neocortex; (4) its presence there is associated with increased phosphorylation of tau; (5) DYRK1A-induced phosphorylation of tau reduces tau's ability to stabilize microtubules; and (6) DYRK1A-induced phosphorylation of tau promotes self-aggregation and fibrillization. Significantly, DYRK1A `primes' tau for additional phosphorylation by GSK3? kinase which is known to contribute to AD pathogenesis. These findings support our hypothesis that inhibition of DYRK1A activity will be disease-modifying and significantly impact on the lives of those with AD. In spite of a role for p-tau in AD pathogenesis, few pharmaceutical industry efforts are targeting the modulation of DYRK1A. Avanti Biosciences is specifically and uniquely focused on DYRK1A and aims to discover small molecule DYRK1A negative modulators derived from natural catechins. The main ingredient of green tea, epigallocatechin gallate (EGCG), is a potent allosteric negative modulator of DYRK1A that results in decreased kinase activity. Unfortunately, EGCG is relatively unstable metabolically and achieves low brain exposure. To discover new catechins that exert the same activity with improved drug-like properties, we characterized the catechins in green tea and discovered that EGCG was not the most potent catechin. In fact, the trans catechin derivatives Gallocatechin gallate (GCG) and Catechin gallate (GC) were more potent, more stable and may achieve better brain exposure. We propose to modify these natural catechins to improve potency, metabolic stability, and brain bioavailability. Selected lead compounds will be validated as negative modulators of DYRK1A activity in vitro and in the rTg4510 tauopathy model. These studies are intended to support future IND enabling studies of potent negative modulators of DYRK1A and eventual AD clinical trials.